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The difference between NPT, BSPP and BSPT Thread

The difference between NPT, BSPP and BSPT Thread

  • 2020/10/28


What is the difference between NPT, BSPP and BSPT Thread?

What is the difference between BSPP, BSPT and NPT? Have you eve confused on these questions? Searching all these information from internet?

As i am engaged in the marine hardware, there will always some questions from my clients: what is the difference between BSPP,BSPT?

There are some easy definition on them.

Pressure systems in the process industry use different ways of sealing depending on the geographical region, size of the pressure system and the environment. There are regional differences in sealing types as well as industry preferences. For example, many pressure systems onboard ships use BSPP adapters while many applications in the oil and gas industry use NPT fittings. While one sealing style is not inherently better than another each style has its application.


NPT Connections

NPT Connections

NPT (National Pipe Thread) seals are the most popular type of seal for pressure calibration systems in the U.S. and Canada. NPT male adapters have a taper thread that wedges into the female NPT adapter. They seal due to the "out of roundness principle" which means that the male stretches the female fitting until there is so much force that the connection can hold pressure. One of the challenges with this design is that if you connect stainless steel to stainless steel then over-tightening or poor lubrication can cause gauling and damage to the threads. Thread sealant is needed to seal but only 2 turns of thread sealant is required. Any more than that and the seal can leak around the thread sealant. Ralston Instruments has a wide variety of male NPT adapters , male Quick-disconnect NPT adapters, male NPT calibrator adapters, female NPT adapters, female NPT gauge adapters and female Quick-disconnect NPT gauge adapters.


BSPT Connections

BSPT Connections

BSPT (British Standard Pipe Taper) is similar to NPT except there are important differences. The angle across the flanks of threads (if you sliced the fitting in half long-ways and measured the angle from root to crest to root) is 55 degrees instead of 60 degrees as it is for NPT. Another important difference is that for many BSPT pipe sizes the thread pitch is different than NPT. Thus an NPT male will sometimes fit into a BSPT fitting or vice versa but they will not seal. This is a popular fitting in China and Japan but is very rarely used in North America unless the equipment to which it is attached was imported. Thread sealant is needed to seal the male and female fitting together. Ralston Instruments has adapters to bothmale BSPTadaptersand female BSPT adapters.


BSPP Connections

BSPP Connections

BSPP (British Standard Parallel Pipe) is most popular in the UK, Europe, Asia, Australia, New Zealand and South Africa. It is a parallel thread fitting that uses a bonded seal ring to do the sealing. This bonded ring seal is sandwiched in-between a shoulder on the male fitting and the face of the female fitting and is squeezed in place. BSPP pressure gauges have a longer male thread and use a copper crush washer that is squeezed in between the bottom of the male fitting and the bottom of the female BSPP hole forming a pressure tight seal. No thread sealant is needed to form a seal. Ralston Instruments has male BSPP adapters , female BSPP adapters, female BSPP gauge adapters, and female BSPP Quick-disconnect gauge adapters.

The marine use hardware THRU HULL with adapter BSPP is well accepted in the market due to the reason description above. The hardware manufacturer produce long enough thru hull fitting and cut for the exact lengthe according to the thickness of the boat hull.


More pictures for checking the difference, check with the website : www.nxymarine.com

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